BACKGROUND: Breath-awareness practices contribute to stress management and psychological well-being among adolescents. However, their neurobehavioural effects remain underexplored, specifically in the Indian developmental context. PURPOSE: This study examined how breath-based Ānāpānasati meditation affects brain electrical activity and the subjective self-reported experiences in adolescent novice meditators posteriori a cognitive workload-inducing task. METHODS: Anapanasati meditation was adapted into a three-stage breath-awareness intervention framework and was administered to 45 novice adolescent meditators. Brain activity was investigated through electroencephalography (EEG), and neural oscillations were measured over the three stages, namely resting state (RS), breath counting (BC) and breath focus (BF). Further, adolescents' breath awareness self-reports were evaluated employing the Amsterdam Resting-State Questionnaire (ARSQ) following the BF stage and the breath count feedback (BCF) after the BC stage. Both the inventories displayed satisfactory psychometric properties, thus facilitating a neurobehavioural analysis in a cross-sectional within-subjects setting. RESULTS: Alpha oscillation was significantly increased throughout the intervention, indicating relaxation. Beta power in both the occipital and midline default mode network (DMN) regions during the count and focus stages exhibited significant positive associations with breath count, suggesting enhanced visual and cognitive processing. Blissfulness felt during counting breaths was also associated with enhanced state mindfulness, sharing a notable negative association with the theory of mind (TOM). State mindfulness further correlated with increased frontal alpha activity, while the theory of mind negatively predicted frontal alpha power. Lastly, exploratory analysis revealed gender differences, with females demonstrating greater frontal beta activity and state mindfulness. CONCLUSION: Breath-awareness meditation can thus be effective for promoting relaxation and blissfulness in adolescents, with possible gender-based variations influencing its impact. Moreover, the positive association of prefrontal alpha with self-reported state mindfulness and its negative association with TOM underscored an inverse interplay between inward-focused mindfulness and outward-directed social cognitive states in adolescents.